0.25-MU-M PSEUDOMORPHIC HEMTS PROCESSED WITH DAMAGE-FREE DRY-ETCH GATE-RECESS TECHNOLOGY

Damage-free, dry-etched 0.25-mum T-shape gate pseudomorphic InGaAs channel HEMT's have been demonstrated. A Freon-12 based discharge was used in either ECR or RIE systems to perform the gate recess process. Etching selectivity of more than 200 was obtained between the GaAs cap layer and the underlying AlGaAs donor layer. Self-bias voltages of -30 to -50 V were used in the etching process to minimize the damage. Pre- and post-etch clean steps were utilized to achieve uniform etch and removal of any dry-etch-related residues. Schottky diodes fabricated on n-GaAs subjected to either dry or wet etching showed no differences of barrier height, zero-bias depletion depth, and ideality factor. By using the dry etch for gate recess, very tight threshold voltage uniformity across a quarter of a 3-in wafer of +/-85 mV was obtained in comparison to +/-300 mV with our conventional wet recess technology. The typical devices showed the comparable I-V characteristics to those fabricated with a wet chemical process. A source resistance of 0.8 OMEGA . mm was measured. The extrinsic transconductance was 437 mS/mm with output conductance of 10 mS/mm.